Bullet weight & recoil

[KJS]

I hear that heavier bullet weights produce more recoil, such as when some fool on Youtube fires his short-barrel .500 Mag with a 700-grain bullet and exclaims "Holly ****!" in response to the massive kick.

I can't say that I've ever noticed any difference, but then virtually everything I've fired has ranged from 130 to 158 grain, so not a huge difference like you find in .500 Mag rounds that I think can go from as low as 275 grain up to a whopping 700 grains. I'm not sure about the physics on this.

It's not at all clear to me why a heavier slug should recoil more since the heavier weight is offset by a lower velocity, so the muzzle energy isn't any greater for the heavy bullet since it's going a lot slower. I'm rather stumped by that one. I'd probably know the answer if I'd actually taken more than one physics class in my entire life.

I asked a friend who's really into shooting and even he wasn't sure. For our benefit, I'm sure the highly experienced gun experts here can enlighten us as to how & why bullet weight impacts recoil.

Thanks.

 

[Mikee Loxxer]

Newton’s Laws will answer this question.

1.A body experiencing a force F experiences an acceleration a related to F by F = ma, where m is the mass of the body.

2.Whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction

 

[KJS]

1.A body experiencing a force F experiences an acceleration a related to F by F = ma, where m is the mass of the body.

2.Whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction.

The bolded part sounds like the "every action has an equal and opposite reaction" as my high school physics class said.

I'm still not getting it. "Force = Mass times Acceleration" makes perfect sense, but after that I run into a problem:

Force = 700 grain mass times relatively slow acceleration

vs

Force = 275 grain mass times relatively fast acceleration

How are the forces different? Is muzzle energy not an accurate way to measure recoil force? The muzzle energy of heavier bullets is generally the same (sometimes actually less) than the muzzle energy of relatively lighter bullets that are flying out of a gun at a higher speed.

I'm still stumped.

 

[1911Tuner]

Go shoot a .220 Swift in a bolt-action rifle that weighs in at about 8 pounds with a 50-55-grain bullet at a mv of approximately 3700-3900 fps.

Then go shoot a .45-70 Sharps carbine of approximately the same weight with a 405-grain bullet at a mv of approximately 1500 fps.

One will nudge your shoulder. The other will ring your bell. Guess which is which.

 

[Mikee Loxxer]

If the acceleration (velocity) stays the same then increasing the mass will result in a greater force (recoil) being acted upon the shooter. If the velocity is reduced yet the mass increases it may or may not increase the recoil. it all depends on what F in the equation is equal to. Increasing the value of either m or a will result in an F of greater value and hence greater recoil.

If you take a 10 pound brick and throw it at a given velocity you will feel a certain amount of force being acted upon you. If you take a 20 pound brick and throw it at the same velocity the force being acted on you will be greater.

The issue is the question of velocity. Is the velocity the same with the heavier bullet or less? That will determine whether or not the recoil increases when using a heavier bullet.

 

[mljdeckard]

Or even a 30-06 bolt rifle. Get 2 cartridges, one loaded with a 110 gr spitzer, and another loaded with a 220 gr bullet, shoot them from the same rifle, one after the other, I promise you will feel the difference.

 

[KJS]

Go shoot a .220 Swift in a bolt-action rifle that weighs in at about 8 pounds with a 50-55-grain bullet at a mv of approximately 3700-3900 fps.

Then go shoot a .45-70 Sharps carbine of approximately the same weight with a 405-grain bullet at a mv of approximately 1500 fps.

One will nudge your shoulder. The other will ring your bell. Guess which is which.

Despite being a gun novice, I'm sure the 405 gr bullet will give quite a kick.

Being a novice, .220 Swift is a caliber I've never heard of, though I know 3,800 ft/sec is exceptionally fast. I think the fastest round I've ever heard of was just over 4,000 ft/sec.

I've also never before heard of a Sharps carbine, though I know a carbine is a rifle with a short barrel (by rifle standards).

 

[RobMoore]

To throw a little mud in the water, sometimes a heavier bullet can mean less felt recoil.

In some shooting competitions, the "power factor" of the round is measured by multiplying the velocity by the weight in grains of the bullet. In the instance of two rounds with different bullet weights that have the same power factor, the heavier bullet is generally going to give the shooter a "softer feel".

 

[azyogi]

you're close by thinking of muzzle energy it's a little more complex the weight ogf the gun also comes into play when talking felt recoil or MG * VG this would be the impulse, or recoil
MG * VG = MB * VB + MC * VC
where MG = mass of the gun
VG = velocity of the gun
MB = mass of the bullet
VB = velocity of the bullet
MC = mass of the powder charge
VC = velocity of the powder charge
quoted from the ballistics section of the NRA Firearms Fact Book [third edition]

 

[mustang_steve]

Break it down into Joules, then it'll make more sense.

X many Joules of energy will produce Y amount more or less than Z Joules of energy.

For sake of point, let's say we have a Muzzleloader. When fired, the gasses push in all directions....since the barrel is a cylinder, the circular section has equilibrium of force, thus no effect in that axis. HOWEVER, the forward and rearward axis is relevant as the gases will try to push the bullet out so it can escape.

This means both the firearm and the bullet are being pushed. The bulk of this is on the bullet, as it's the lighter object. the firearm sees a lesser force, which is our recoil.

So the more joules of energy is involved, the more recoil.

 

[1911Tuner]

KJS...I wanted to establish in your mind that bullet velocity is only one aspect of recoil.

To simplify my analogy...

The 405-grain bullet requires more force to accelerate from zero to 1500 fps than the 55-grain bullet requires to accelerate to 3800 fps.

Whatever force is delivered in one direction is delivered in the other...in equal measure. Or...another way...Force forward equals force backward. I'll go get a picture of a Sharps carbine for ya. Stand by.

The .220 Swift is a .22 caliber centerfire based on the old 6mm Lee Navy cartridge...necked down to accept the smaller bullet...it was king of the .22 bore speed hill for a long time...and probably still is.
I've seen a few .220 Swift rifles break the 4,000 fps barrier. I don't keep up with the little bores and varmint rifle calibers any more...so that may have changed.

Anyway...The 1859 Pattern Sharps Cavalry Carbine.

 

[1911Tuner]

This means both the firearm and the bullet are being pushed. The bulk of this is on the bullet, as it's the lighter object

Steve...No. Rifle and bullet feel equal force. Force is force, and is the same in all directions. If 25,000 units of force are on the base of the bullet...the same 25,000 units are on the breechblock.

 

[KJS]

If the acceleration (velocity) stays the same then increasing the mass will result in a greater force (recoil) being acted upon the shooter.

I agree 100%. A .30-06 & .50 BMG produce roughly the same velocity, though the .50 BMG is going to have a hell of a lot more recoil as it launches a vastly heavier bullet.

But velocity doesn't stay the same for any given caliber as weight changes. Heavier bullets (of the same caliber) will tend to be slower. Quoting from a ballistics chart of Remington ammo:

I'll use their .45 ACP as a randomly selected example:

-185 gr has a muzzle velocity of 1,015 ft/sec & 423 ft/lbs of energy.
-230 gr has a muzzle velocity of 853 ft/sec & 356 ft/lbs of energy.

The heavier bullet moves slower & actually packs less energy than the one that's 20% lighter.

If you take a 10 pound brick and throw it at a given velocity you will feel a certain amount of force being acted upon you. If you take a 20 pound brick and throw it at the same velocity the force being acted on you will be greater.

I agree 100% again.

 

[1911Tuner]

KJS...bullet energy doesn't determine recoil. Rate of acceleration and applied force does. Go back and read my last post...the one with the purty picture.

 

[KJS]

the weight ogf the gun also comes into play

Yes, certainly. I have a Ruger .357 Mag with a 6" barrel that weighs 45 ounces unloaded. This muzzle-heavy beast absorbs recoil quite nicely. I've never fired .357 in any other gun, but I trust that doing so with some snub-nose fancy alloy S&W .357 that gets as light as 12 ounces would be a brutal endurance contest where I'd lose.

 

[mustang_steve]

Steve...No. Rifle and bullet feel equal force. Force is force, and is the same in all directions. If 25,000 units of force are on the base of the bullet...the same 25,000 units are on the breechblock.

You're right, not the first time I screwed that stuff up. At least the rest of the firearm will distort some and reduce some of the energy you'll experience at your hand or shoulder depending on the firearm used.

 

[1911Tuner]

At least the rest of the firearm will distort some and reduce some of the energy you'll experience at your hand or shoulder depending on the firearm used.

Well...yeah, by way of the gun's mass. The heavier/more massive the gun, the better it soaks up your perception of recoil. It "feels" less sharp...but only because it accelerates at a slower rate than a lighter gun. In the absence of outside force, both gun and bullet momentum are equal during the actual action/reaction event...while the bullet is in the barrel and under an accelerating force.

Once the bullet exits...the force is removed from the system, and there is no more acceleration...thus no more recoil. Any further movement of either part of the system is due to momentum conserved during the acceleration on the system.

Again...to address the original question...Force forward=force backward. The harder one side is pushed, the harder the other side is pushed. It's entirely possible to get more recoil from a light bullet...if it's pushed hard enough. Or...if enough force is imposed on the system to generate a higher recoil impetus. It's all about force and acceleration. Bullet energy doesn't determine recoil force.

The actual mechanical action/reaction recoil only lasts for a brief instant. As in...How long does it take the bullet and the gas ejecta to reach the muzzle. It's over so fast that we scarcely have time to detect it...or at least we can't separate the actual punch of recoil from the after effects...the momentum.

 

[AirborneNCO]

Hey KJS, check out this link:

http://www.handloads.com/calc/recoil.asp

It's a recoil calculator. I can't say anything about its credibility, but I played around with it some. I put in a 55 grain bullet on the left with a muzzle velocity of 3000 fps, then put in a fictional 75 grain bullet in the comparison with it at a tailored proportion of 2200 fps (I did the math to see what percentage smaller the velocity would have to be to match the weight difference proportion of the two bullets). Then I put in identical powder grains for both and the same firearm weight of 8 pounds. Granted, this is an unlikely configuration, but I'm doing it for experimental purposes here. Interestingly, the recoil figures came out to be identical for both sides. According to this calculator, if it is correct, recoil seems to be a function of bullet weight, velocity, powder charge, and the weight of the firearm, roughly. I ran that through my common sense meter and it came out okay so far. So based on that, yes, the velocity and weight differences make up for one another to a certain extent, but the amount of powder and firearm mass also plays a key role. Also, in most cases I'd expect that even though there's a trade off of weight and velocity, it won't coincidentally end up being so perfectly proportionate that the recoil ends up exactly the same unless the loader intended for it to be that way. That being said, in many cases I'm sure the trade off is way out of proportion with regard to how it translates into recoil. The extreme case of this, for example, would be the 220 swift vs. 405 sharps example that 1911 mentioned. So the felt recoil depends on how big of a proportion change your dealing with regarding those factors.

From my experience, there was one instance in which this kind of stuff came to my attention. I had purchased a Sig P226R blackwater edition, and was shooting 115 grain 9mm bullets out of it that work fine in my Beretta 92FS. I thought there was a malfunction because the slide wasn't locking back after the last round was fired from the magazine. :banghead: However, when I fired 147 grain bullets from it, it worked perfectly every time. I soon realized that the recoil blowback from the 147 grain bullets and powder combination was greater than that of the other round enough to make a difference in whether the slide locked back. I didn't know whether to be pleased that I'd learned something, disappointed, or confused. I guess the Sig is built more robustly and has a more massive slide and spring, and requires more recoil to operate properly.

 

[1911Tuner]

The extreme case of this, for example, would be the 220 swift vs. 405 sharps example that 1911 mentioned. So the felt recoil depends on how big of a proportion change your dealing with regarding those factors.

Bingo. That was an extreme for illustrative purposes. If you start with an 8-pound rifle in .308 caliber...and load to equal pressures with the same powder...with a 150 and a 165 grain bullet...the reality is that you'll never detect the difference in a blind back-to-back test.

 

[kludge]

1911Tuner has it exactly right.

I probably can't improve on anything already written, but you can also think of it this way:

You have a barrel with two bullets in it that is open on both ends. This barrel is balanced and hanging by a string. The bullets are pointing opposite directions, and there is a powder charge between them and everything is perfectly centered in the double-ended barrel.

Now set off the powder charge.

The powder charge will create a pressure (a force) and both bullets, assuming the have equal mass begin to accellerate at the same rate in opposite directions.

The pressure from the gasses created push equally in all directions, but the bullets are the only thing in this system that can move - so they do. The pressure exterted on the insides of the barrel pushes equally left and right, up and down, so the barrel has to be rigid and strong enough to contain the pressure, but since the forces left and right and up and down cancel out the barrel does not move.

The two bullets now exit each end of the barrel simultaneously and the pressure is relieved and the bullets go on their merry way. BTW, I measure the velocities and acceleration and they are equal, as expected.

Now this doesn't make a very useful gun. I want a projectile going away from me but not one toward me; so I remove one of the bullets and in its place I put a metal slug, and drill it though and put a pin in it. I then balance the barrel contraption and hang it by a long string. Now I load another powder charge and put another bullet in place (only one this time) and set it off.

As it turns out I've designed a space age metal that is very light and strong, and the barrel mass is identical to the bullet mass...

And then I set off the charge.

This time I measure the bullet velocity and acceleration, and it is the same as before, but this space age barrel is coming backward at me just as fast as the bullet was before... this won't work so I keep trying...

I keep adding mass to the barrel and I discover that as I add more mass the barrel it slows down and the bullet speeds up. Eventually though I get to a point of diminishing returns.

I've been mesuring velocities and accelerations of the bullets and the barrel contraption and I discover that one thing always holds true:

Mass(bullet) X Acceleration(bullet) = Mass(gun) X Acceleration(gun)

The more powder I use the bigger my acceleration numbers are.

.
.
.

When comparing recoil of heavy and light bullets, some variable come into play...

When using light bullets you can use more powder which gives you even faster acceleration of the light bullets (also increasing the force of the recoil).

When using heavier bullets (which accelerate more slowly) the duration of the force that creates recoil is increased.

It's the strength of the force (pressure) and "dwell time" (the time the bullet is in the barrel) that determines the recoil... the longer the bullet is in the barrel the more the gun can accelerate, and the more momentum it will have after the bullet leaves the barrel.

With an equal amount of force, shooting the heaver bullet will increase the amount of recoil, but as long as your going to use a lighter (shorter) bullet you might as well cram more powder in the case, and the pendulum starts to swing the other way...

If you want to feel some hard recoil try a .454 casull with 325gr bullets at 1500fps. If you want it to sting try some 240gr bullets at 1800fps.


ETA:

FWIW, "low-recoil" ammo usually uses light for caliber bullets.

 

[Zoogster]

I think I understand why you are perplexed.

It's not at all clear to me why a heavier slug should recoil more since the heavier weight is offset by a lower velocity, so the muzzle energy isn't any greater for the heavy bullet since it's going a lot slower. I'm rather stumped by that one.

You are correct that muzzle energy is a poor way to compute recoil, even if the firearms both weigh the same.

A heavy slow projectile will have more recoil for the same muzzle energy.
It is simply harder to get a heavy object moving.



A much more effective way to compare recoil is through momentum rather than energy. (I also think momentum is a much more effective way to determine the overall power of rounds going below around 2,500-3,000 FPS. Above that rifle ballistics are very different.)

For example take the 7.62x51 NATO loading of 146.6 grain projectile at around 2,756 FPS from a standard barrel. It gives you just short of 2,500 foot pounds of energy at the muzzle. (2472 foo pounds of energy.)
Now a foster shotgun slug weighing one ounce (437.5 grains) of 438 grains traveling 1600 fps gives you just short of 2,500 foot pounds of energy at the muzzle. (2489 foot pounds of energy.)

So in energy figures they are about the same at the muzzle, around 2,500.
Yet the shotgun is going to have significantly more recoil.
What is the momentum of the two rounds?
The 12 gauge projectile has a momentum of 100. While the 7.62x51 projectile has a momentum of 57.

Then the weight of the firearm will significantly alter the felt recoil. The hardest recoiling firearms are often lightweight rifles meant to be carried long distances chambered for big game.
For that reason many elephant guns, for example a 14 pound .577 A-Square Tyrannosaur will recoil much harder than say a 50 BMG chambered Barret weighing over 30 pounds, even though they are firing a round with less energy.
A .50 caliber Barret weighing in at around 30 pounds recoils similar to your typical 12 gauge weighing around 7-8 pounds. Yet carrying a 30 pound rifle around all day is certainly not enjoyable, especially combined with a full load of other gear.

Even a small amount of increased weight in the firearm significantly reduces felt recoil. Two firearms chambered in the same cartridge will feel very different if they are a few pounds different.
It is the same for handguns. Try one of the Scandium frame .357 magnums or .44 magnum handguns which typically weigh much less than thier steel counterparts. The felt recoil is significantly greater. Yet the difference between the two is typically less than 1 pound.

 

[ConstitutionCowboy]

A minor but important point: The heavier bullet will take longer to accelerate down the barrel, therefore, felt recoil will last longer. With a light bullet, even with a slightly larger powder charge allowable since the pressure won't rise beyond limits due to the fact that the bullet moves faster creating volume behind it faster than the heavier bullet, the felt recoil won't last as long. Since acceleration is a function of time squared, the felt recoil will be greater for the heavier bullet with all else being more or less equal.

Does that help?

Woody

 

[tjj]

Man, my head hurts.
Heavier bullet = higher moment of inertia
Force required to overcome that moment of inertia will result in more recoil

 

[1911Tuner]

Heavier bullet = higher moment of inertia
Force required to overcome that moment of inertia will result in more recoil

Bingo. Don't forget to factor in friction. A longer/heavier bullet presents more surface area to the bore...assuming that both bullets are of the same type. i.e Boattail or plain base.


Cowboy! Correct...but...unless the two examples are at extremes...you'll never be able to tell the difference. i.e a 165-grain bullet is 10% more massive than a 150.

When we're talkin' a small few thousandths of a second to reach the muzzle...10% more ain't a helluva lotta difference. By the time your brain registers a recoil impulse...the bullet is gone and the recoil is over.

 

[ConstitutionCowboy]

1911Tuner

Agreed. But, if you compare a 308 Winchester with a 110 grain bullet to one with a 200 grain, keeping the CUP around 49,000, you'll notice the difference.

Woody